The term active microstructural elements is intended to refer, for example, to elements of the microelectronics sector (such as transistors, diodes, metal-insulator-metal elements), image elements and displays, electrode structures of micromechanical sensors and actuators as well as elements which emit particle radiation (for example, light or electrodes), such as laser diodes or field emission tips.
Microstructural elements of that type are produced as a plurality on a substrate, for example, wafers or glass plates. In the microstructural technology sector, mechanical, optical, electrical and other elements are produced using methods and processes which have been known for some time in the microelectronics sector. Accordingly, the known errors also occur during production, caused, for example, by contaminants or misalignments. In order to be able to ensure a fault-free function for the microstructural elements, therefore, it is necessary to test the function of every individual element. However, testing microstructural elements places special requirements on the method used and the corresponding apparatus owing to the small dimensions.
Microstructural elements of the microelectronics sector are usually tested on the wafer in that probe tips contact the individual elements (chips) and subject them to a sequence of electrical tests. Contact-free methods using particle radiation are known, for example, from U.S. Pat. No. 3,531,716 owing to the rapid measurement of the electrical functions of transistors, lines as well as capacitors and resistors. Those known methods are substantially based on the fact that the electrical charge at a specific point of the component is measured by means of released secondary electrons using an electron beam.
Another method utilizing the contact-free technology is known, for example, from EP-B-0 523 594, in which the function of elements in liquid crystal displays is tested. That method uses particle radiation, preferably an electron beam, both for the charge measurement and for the supply of current to the display elements.
However, all known contract-free methods detect malfunction-free elements as malfunctioning if the error thresholds for the evaluation are set too close to the desired values of the measurement signals. On the other hand, if a sufficient difference between the desired values and threshold values is set, malfunctions might not be detected. Furthermore, only result data within a very restricted range are available for malfunction classifications as a result of the conventional tests.